docs: update README.md

Author: allcontributors[bot]

README.md

@@ -75,6 +75,7 @@ Check [all 59 challenges](https://angular-challenges.vercel.app/)
       <td align="center" valign="top" width="14.28%"><a href="https://github.com/michalgrzegorczyk-dev"><img src="https://avatars.githubusercontent.com/u/47832176?v=4?s=100" width="100px;" alt="Michał Grzegorczyk"/><br /><sub><b>Michał Grzegorczyk</b></sub></a><br /><a href="https://github.com/tomalaforge/angular-challenges/commits?author=michalgrzegorczyk-dev" title="Documentation">📖</a></td>
       <td align="center" valign="top" width="14.28%"><a href="https://github.com/tamim36"><img src="https://avatars.githubusercontent.com/u/42251521?v=4?s=100" width="100px;" alt="Tamim Arefin Anik"/><br /><sub><b>Tamim Arefin Anik</b></sub></a><br /><a href="https://github.com/tomalaforge/angular-challenges/issues?q=author%3Atamim36" title="Bug reports">🐛</a></td>
       <td align="center" valign="top" width="14.28%"><a href="https://github.com/WhoisBsa"><img src="https://avatars.githubusercontent.com/u/36895235?v=4?s=100" width="100px;" alt="Matheus B."/><br /><sub><b>Matheus B.</b></sub></a><br /><a href="https://github.com/tomalaforge/angular-challenges/issues?q=author%3AWhoisBsa" title="Bug reports">🐛</a></td>
+      <td align="center" valign="top" width="14.28%"><a href="https://sourcerer.io/stefh"><img src="https://avatars.githubusercontent.com/u/249938?v=4?s=100" width="100px;" alt="Stef Heyenrath"/><br /><sub><b>Stef Heyenrath</b></sub></a><br /><a href="https://github.com/tomalaforge/angular-challenges/commits?author=StefH" title="Documentation">📖</a></td>
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